Drought Stress on Trees Deeper Than is Evident

RANDALL DICKERSON | Associated Press

NASHVILLE, Tenn. (AP) — Tulip poplar trees are dropping yellowed leaves, white pines are shedding second-year needles months early and the depth of damage to Tennessee's trees from the current drought might not be immediately evident.

"The old, the young and the weak are more likely to succumb than those that are healthy, established trees," said Dr. David Mercker, a forestry specialist with the University of Tennessee Extension in Jackson. "It could be a year or two before you see a noticeable decline."

That said, there is already adequate evidence that trees are in trouble and the rain that fell this week across much of Tennessee was not a drought breaker.

"We're seeing a lot of mature trees that are flagging out and dying," said Tom Simpson, regional urban forester with the state Forestry Division, from Sevierville. "Up on dry ridges, those facing south, we're seeing 20-inch diameter trees dying."

The severity of stress that trees can handle depends on several factors beyond age and health. The soil they grow in matters. River bottom land is better than dry ridges.

Species is also a factor. Mercker said among the more drought-tolerant varieties are generally those with smaller leaves. Among them: most oaks, red cedar, loblolly pine, black gum, persimmon, hickory, hollies, sassafras, hackberry and sumac. Among types of trees at greater risk are poplar, birch, sycamore, sugar maple, black cherry, beech and cottonwood.

Where in the state the tree is growing is also an issue. The severity of the drought deepens as one travels from east to west across Tennessee. The latest assessment showed northern counties in Tennessee from the Mississippi River into the Clarksville area in extreme drought while the balance of West Tennessee and most of Middle Tennessee were shown in severe drought. Most of East Tennessee ranged from abnormally dry to moderate drought.

Forestry experts and meteorologists say recent rain, welcome as it is, will have little effect.

Conditions are expected to intensify through September between the Mississippi River and the eastern edge of the Cumberland Plateau. Drought conditions are projected to develop up the eastern Tennessee River Valley and the mountains into the state's northeastern corner.

Mercker said the early stress that is evident doesn't necessarily mean a tree is dying.

"They can go into a dormant stage, like a bear in hibernation," Merck said. "Trees will overproduce leaves and can drop some without being harmed."

If the drought wears on, though, root hairs and the ends of branches start dying and that could indicate the tree could succumb next year.

People trying to aid trees planted in their yard should kill all grass out to the edge of the tree's canopy cover — the "drip line" — and mulch that bare earth a couple of inches deep.

"Shallow but wide," is Mercker's advice.

He said a deep "volcano" of mulch right around a tree's trunk isn't of much value to it. Making the area under the tree more like a forest floor and then watering is the best aid. Avoid fertilizing during drought.

According to the latest forestry survey, 50 percent of Tennessee is covered in forest. A lot of woodland creatures live there and the winter ahead is going to be tough for them, with poor production of what is called "hard mast".

"It's going to be harsh on wildlife," Mercker said. "Acorns and nuts will abort early or be very small."

Over in the mountains, Simpson is worried about the fall.

"Our fire season generally picks up in October, but we're having a rash of wildfires now," he said.

Firefighting crews have been working almost continually in Sevier, Cocke, Blount and Monroe counties in recent weeks.

In past summers, the division has sent firefighting crews to other states to help battle large fires. This summer, they're needed at home.

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